The advent of X‐ray lithography as a natural compliment to electron beam pattern generation and photolithography seems to be filling a need in the fabrication of submicron devices. The X‐ray technique, which is simple for single level devices, lags behind other lithographies in registration techniques. However, its proven high resolution capabilities is responsible for the increased interest in further development. At present a, variety of mask substrates are being evaluated with no one material exhibiting an overwhelming advantage. The type of substrate used is closely coupled to the permissable wavelength of the X‐ray source. The X‐rays used for lithography to date vary from Rh L (4Å) up to CK (44Å). Each wavelength shows a distinct advantage and disadvantage. For example, at short wavelengths substrates can be relatively massive but resists are less sensitive and high resolution masks have low contrasts. At longer wavelengths, resists are more sensitive and masks have higher contrast, but defects due to dust are more probable. The use of more than one X‐ray source could fulfill the requirements imposed by mask making and device fabrication. High throughput for both masks and device require both foster resists and higher intensity X‐ray sources. Copyright © 1977 Society of Plastics Engineers, Inc.